Uncovering the Role of Critical Bonds in the Thermomechanical Response of Zn(1,4-benzenedicarboxylate)(1,4-diazabicyclo[2,2,2]octane) Using Simulations and Physics-Constrained Neural Networks.
Journal:
Langmuir : the ACS journal of surfaces and colloids
Published Date:
May 7, 2025
Abstract
Metal-organic frameworks (MOFs) are susceptible to harsh conditions involving high temperatures, mechanical loading, host/guest chemical interactions, or a combination thereof due to the disruption of underlying bonds. Here, we probed the thermomechanical response of Zn(BDC)(DABCO) (BDC = 1,4-benzenedicarboxylate and DABCO = 1,4-diazabicyclo[2,2,2]octane) MOF or Zn-DMOF, whose metal nodes are connected to two BDC and DABCO linkers via Zn-O and N-Zn bonds, respectively. We have examined the relative contributions of such bonds toward Zn-MOF's thermomechanical response at 200 and 300 K, by training a physics-constrained neural network with molecular dynamics (AIMD)-derived interatomic vibration data, and quantitatively estimated interatomic bond strengths within a local environment in the MOF body. We quantitatively show that N-Zn and Zn-O bonds near the Zn-based metal nodes are weaker than their surroundings. These findings were followed up by separately annealing Zn-DMOF at 920 K-AIMD (above its thermal decomposition temperature), mechanically straining it to failure using 0 K-DFT, and examining host/guest interactions in aqueous and acidic environments with 300 K-AIMD. Together, they indicated that structural instability in Zn-DMOF was initiated by the disruption of N-Zn and Zn-O bonds under harsh conditions and that Zn-O bonds are weaker than N-Zn bonds at ≥ 300 K. Broadly, we show that bond strength estimates are a reasonable indicator of Zn(BDC)(DABCO)'s performance at high temperatures and mechanical loading, and demonstrate the viability of employing AIMD simulations and physics-constrained neural networks to quantify interatomic bond strengths of hybrid organic-inorganic materials.
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